Airline companies ordering aircraft typically specify a number of options, including passenger seating layout. Manufacturing and inventory costs incurred in providing different seating arrangements and spacing between seats are significant. This problem is of greater concern in newer generation aircraft in which a passenger service system and an optional entertainment system may be installed in the back of each seat. Using conventional techniques, an aircraft manufacturer would be forced to inventory and install different length power lead harnesses to supply power to the seats for each seating arrangement. The cost and weight penalty associated with such a requirement would likely be unacceptable to most passenger carriers.
An alternative to wiring each seat to a power source is disclosed in commonly assigned U.S. Pat. No. 4,428,078 (C. Kuo). This patent discloses what is referred to therein as a "wireless system" for supplying power to a plurality of multiple turn pickup coils disposed in the base of seats throughout an aircraft cabin. Perhaps a more accurate term would be a "connectorless" system, since power is inductively coupled from a power supply loop that is disposed in the floor of the aircraft cabin to the pickup coils without the use of a direct electrical connection. This connectorless system permits the seats to be moved about in different arrangements without concern for interconnecting wiring. Not disclosed in the patent are details concerning the regulation of voltage at each of the distributed loads that are inductively coupled to the supply loop.
The connectorless power distribution system described in the above patent has been further developed, and now includes a precisely controlled constant current source driving a series resonant supply loop. Each of the pickup coils is loosely coupled to the supply loop, with a coefficient of coupling in the range from 0.01 to 0.10. The leakage inductance of the supply loop and of each pickup coil is very large compared to their mutual inductance, and is the source of most of the voltage drop of the power source. A series resonant capacitor is provided to nullify the leakage inductance of the supply loop, leaving only the resistance and mutual inductance to impede primary current flow. Since the mutual inductance of the pickup coils appears in series in the supply loop, the constant current source can only maintain a constant voltage at the output of the pickup coil so long as the mutual inductance and load remains constant. However, the mutual inductance is inversely proportional to the distance between the supply loop and the pickup coils, and the distance may vary significantly. In addition, the electrical load on each pickup coil may vary over a relatively wide range. Because of these variable parameters, a regulator must be provided for each pickup coil to maintain a constant voltage across its load.
Design of an appropriate regulator may initially seem a trivial problem. For example, a series pass regulator admittedly could be used to regulate the voltage across each distributed load. However, the efficiency of such a regulator circuit would be relatively low. In addition, high peak currents from any capacitive filter used upstream of the load would be reflected back to the supply loop, causing unacceptable electromagnetic interference (EMI) and possible disruption of the constant current source. Similar problems would likely arise if a switching regulator was used. Shunt regulators, such as a "Q spoiler" could be used to regulate the voltage on the pickup coil by providing a controlled shunt across the tank circuit, in a feedback loop. Unfortunately, shunt regulators tend to be highly dissipative, and such regulators would typically involve a high part count and unacceptable cost factor.
In consideration of the above-described problems, it is an object of the present invention to provide a low-cost regulator for each load of a connectorless power distribution system. It is a further object to partially compensate the leakage inductance of the pickup coils comprising the system, using the residual leakage inductance to ferroresonantly regulate the voltage across the load. Another object is to provide a buffer between the supply loop and the pickup coils. A still further object is to protect the supply loop against short circuits. These and other objects and advantages of the present invention will be apparent from the attached drawings and the Description of the Preferred Embodiments that follows.